Such flap devices serve, for example, as exhaust gas retention flaps or as exhaust gas feedback flaps in the exhaust gas system of an internal combustion engine. The exhaust gas contains pollutants which must not be released to the outside so that a reliable sealing must be provided along the shaft that protrudes outward towards an actuator. This sealing must function perfectly at any time and under varying thermal stresses. A precise controllability must also be maintained with the flaps in order to meet the emission regulations for modern internal combustions engines.
Various flap devices have previously been described which attempt to attain these goals. DE 20 2008 005 992 U1 describes a flap valve supported on two sides for use in the hot gas zone of exhaust gas systems in which a seal arranged on an oblique shoulder of the shaft is pressed against an opposite sealing surface of the housing by a spring force. The sealing point simultaneously serves to axially secure the flap valve. A closing of the flap as well as an occurring thermal expansion may jam the flap in the cannel due to the flaps being centered in the channel.
An exhaust gas flap is also described in U.S. Pat. No. 5,630,571 wherein a steel disc is mounted on the shaft behind a bearing bush, which disc is concavely shaped at its end averted from the flow channel and which abuts on a correspondingly convexly shaped ceramic disc. The latter abuts on a bush with its flat opposite axial end, which bush is mounted in a press-fit at the bore, the bush extending beyond the end of the flow housing. A disc is mounted on the end of the shaft, which disc serves as a lever to actuate the flap. A wave spring is arranged between the disc and the bush, via which the steel disc is pressed against the ceramic disc for sealing and a shoulder of the shaft is pressed against the first bearing bush.
When thermal expansion occurs or when tolerances are provided with insufficient precision, the consequence is that either the sealing faces of the ceramic disc no longer abut on the steel disc with sufficient strength, or the position of the flap in the channel is no longer sufficiently fixed, which may lead to a jamming of the flap in the channel. An increased wear of the wave spring also results since a relative movement exists between the disc carrying the lever and the second bush, which results in a movement along the spring surface.
The known designs therefore have drawbacks in that, when thermal conditions change, a sufficient sealing and an adjustability of the flap are not provided without a risk of jamming.